As Donald Trumpwarned last month, amid news that the F.B.I. had begun investigating the Trump family’s finances, the president has “complete power” to issue pardons—and he isn’t afraid to do so. On Friday night, as a massive hurricane bore down on Texas, the president offered an official pardon for Arizona sheriff Joe Arpaio, who had been convicted of violating a court order not to racially profile and illegally detain Latinos on suspicion of being undocumented. Even Republican lawmakers were appalled: Senator John McCain, who represents Arizona, tweeted “@POTUS’s pardon of Joe Arpaio, who illegally profiled Latinos, undermines his claim for the respect of rule of law.” House Speaker Paul Ryan denounced the move in a statement suggesting that the pardon might lead law enforcement officers to think they can violate civil rights.

For the president, however, the calculus seemed simple: Trump likes Arpaio because Arpaio likes Trump. America’s “toughest sheriff” was one of Trump’s most voluble supporters on the campaign trail; both men are “birthers” who frequently praised each other’s efforts to prove the unfounded claim that Barack Obama was not born in the United States; and both share an affinity for inflammatory rhetoric about illegal immigration. (Arpaio famously housed prisoners in tent camps in the desert, where temperatures often rose well above 100 degrees; Trump praised him for having “kept Arizona safe!”)

The far-right appeared to be pleased with the decision. But the Arpaio pardon also sends a signal beyond Trump’s nativist base. As The Washington Postreports, Trump was planning to pardon Arpaio even before his case went to trial:

The president asked Attorney General Jeff Sessions whether it would be possible for the government to drop the criminal case against Arpaio, but was advised that would be inappropriate, according to three people with knowledge of the conversation. After talking with Sessions, Trump decided to let the case go to trial, and if Arpaio was convicted, he could grant clemency.

The president was “gung-ho about it,” according to one associate. He also demonstrated, as he previewed with his “complete power” tweet in July, that he will move aggressively, and unilaterally, to protect political allies from prosecution or sentencing. That could pose a serious problem for the F.B.I. probe, led by special counsel Robert Mueller, as prosecutors potentially seek to cut deals with Trump associates in exchange for testimony against the president or members of his inner circle. Mueller has already impaneled a grand jury and begun issuing subpoenas, and raided former Trump campaign manager Paul Manafort’s home last month. But all those shock tactics could be neutralized if potential state witnesses believe that the president could pardon them in exchange for their silence. (Manafort has repeatedly insisted that he is cooperating but not testifying on behalf of Mueller’s investigation.)

While presidents have traditionally used the pardon power sparingly, and suffered political blowback when the power is abused, Trump has just sent a clear signal that he will not be constrained by elite opinion or the disapproval of Republican leadership. Nor will he wait for his friends or associates to be charged or sentenced before pardoning them. Still, there are limits to Trump’s ability to meddle in Mueller’s investigation. As the Post noted back in June, anyone who is pardoned for a potential crime cannot then assert their Fifth Amendment right against self-incrimination, effectively stripping them of their right to refuse to testify against a colleague. Applying the Arpaio principle to the Russia probe could backfire in other ways, too: Any move Trump makes to interfere in the legal process could be further evidence of obstruction of justice, should that charge be brought against him. If Congress decides they have had enough, there is no executive authority Trump can exercise to save himself from impeachment.